The performance of wireless transceivers relies heavily on the performance, e.g., linearity, efficiency, etc., of the amplifiers used by the wireless transceivers to amplify signals, e.g., for subsequent transmission. In order for a power amplifier to achieve good power efficiency, the voltage-swing of an input stage of the power amplifier needs to be relatively high. Typically, attaining such a high input voltage-swing while also maintaining good linearity at the input stage requires some kind of linearization circuitry in addition to the power amplifier circuitry. Further, to avoid compression and amplitude nonlinearity, voltage variations at the input stage need to be as small as possible. In practice, these goals require the amplifier to be implemented with large transistors, which is not ideal.
Digital pre-distortion and closed-loop polar architecture represent two types of conventional solutions for improving the linearity of a power amplifier. With a closed-loop polar architecture solution, the output of the power amplifier is down-converted based on a gain control and then compared with the phase and magnitude of the signal used to drive the power amplifier. Using such a closed-loop polar architecture solution may significantly reduce variations in the load, temperature, etc., of the power amplifier. However, the costs of such a solution are increased design complexity, larger chip area, and increased power consumption. With digital pre-distortion solutions, the nonlinearity of the power amplifier is first measured during calibration, and the input signal is pre-distorted properly to compensate for the measured power amplifier nonlinearity. While pre-distortion solutions may be less complex, require a smaller chip area, and may use less power relative to closed-loop power architecture solutions, digital pre-distortion solutions are sometimes less effective, especially when the system needs to operate in changing conditions, e.g., changing environmental conditions. Thus, there remains a need for improved linearization solutions that achieve a desired effectiveness over varying operating conditions without overly increasing the complexity, size, and/or power of the associated amplifier system.